“Star Trek-style teleportation may one day become a reality. You step into the transporter, which instantly scans your body and brain, vaporizing them in the process. The information is transmitted to Mars, where it is used by the receiving station to reconstitute your body and brain exactly as they were on Earth. … But wait. Do you really step out of the receiving station on Mars? Someone just like you steps out … But perhaps this person is merely your replica.”